1. Field of the Invention
The invention generally is a process and apparatus for the treatment, remediation, handling, and disposal of hazardous wastes containing elemental phosphorus. The invention more specifically is a process, referred to as high speed air dispersion (HSAD), which is fast, simple and cost effective for complete conversion of the P.sub.4 -pollutants to strongly acidic solutions which may react and/or fix other leachable toxic heavy metal contaminants in the sludge or soil residue, thereby remediating a P.sub.4 -pollutant containing material, and an apparatus for use in the process for remediating the P.sub.4 -pollutants.
2. Prior Art
Numerous methods have been explored for removing phosphorus and phosphorus oxy-compounds from municipal and industrial wastes, such as phosphorus sludges, phosphorus-containing soil, and phosphorus-containing waste waters (often referred to as phossy water). However, data regarding the removal of elemental phosphorus from phossy water and phosphorus sludges are rather limited. An extensive literature review on this subject was made by J. D. Fleming, Removal of Phosphorus, A Literature Survey, Tennessee Valley Authority, Muscle Shoals, AL (1970 TVA Report). Most of the reported techniques involve the removal of dissolved phosphorus by chemical precipitation, ion exchange, reverse osmosis, bacterial treatment, and combined chemical-biological treatment. This prior art includes several chemical and physical processes for treating phossy water and P.sub.4 sludges. The chemical treatment methods include air oxidation, chlorine oxidation, electrolytic oxidation, catalytic oxidation, distillation, and CS.sub.2 extraction. The physical methods include sizing, sedimentation, centrifugation, cycloning, and flotation. In most of these processes, phosphorus is only partially separated or oxidized from the solid impurities, or high temperatures are needed to volatilize elemental phosphorus and water leaving a phosphorus free residue.
A waste water treatment method is disclosed in an article by J. C. Barber in Chemical Engineering Progress, Vol. 65, No. 6, June 1969, entitled Waste Effluent Treatment and Reuse. In this method the elemental phosphorus is reduced from 1.5-2.4 ppm to about 0.05 ppm in a combined clarification and chlorination technique to remove elemental phosphorus from phossy water. Unfortunately, the toxic nature of the residual chlorine in the resulting waste water is disadvantageous and limits the usefulness of this technology. The oxidation of phosphorus in the phossy water with air is reported in the article, specifically laboratory tests made with 134-492 cubic ft. of air/1,000 gallons of waste water oxidized about 63-86% of the phosphorus leaving 0.3-0.7 ppm P.sub.4 in the aerated water. The article reports that neither the time of aeration nor the volume of air used affects the extent of oxidation and this method does not provide a complete phosphorus removal treatment. No details are given regarding the method and intensity of pulp mixing.
U.S. Pat. No. 4,686,094 discloses a process of treating pyrophoric phosphorus-containing material with oxygen-containing gas to convert it to substantially less pyrophoric form while otherwise protecting the pyrophoric phosphorus with a blanket of non-flammable fluid (i.e. water). This method makes no mention of high shear agitation and is shown to remove only 95% of the phosphorus in the sludge after six months reaction. On the contrary, the present invention results in up to 100% phosphorus removal in as few as 100 minutes or fewer.
U.S. Pat. No. 3,515,515 discloses the use of an oxidizing agent in the reduction of phosphorus from phosphorus-containing sludge. However, this reference teaches the use of compounds other than oxygen as the oxidizing agent. In addition, the '515 patent utilizes agitation with agitator speeds being two orders of magnitude lower than the present invention, resulting in significantly less intimate mixing and contact between the sludge and the oxidant, and significantly less phosphorous removal.
U.S. Pat. No. 3,650,950 discloses an apparatus for shear mixing and aeration of sewage. The '950 patent describes the use of a critical shearing zone into which ozone, air, or oxygen are injected, but claims an active agent as the oxidative species. The '950 patent discloses that shearing of the waste material makes it more receptive to dissolved oxygen, microbial or bacterial action, oxidation of solids and aeration. In addition, the '950 patent discloses that high solids loadings then become possible. However, no mention is make of the specific use for recovering phosphorus from phosphorus-containing sludge, and was developed for conventional sewage treatment.
U.S. Pat. No. 2,138,349 discloses a method of aeration of sewage involving top-to-bottom circulation of the medium and bubbling of oxygen through the medium. The '349 patent does not disclose the use of high shear mixing to distribute the oxygen; however, it does mention that an important step in the aeration of sewage is agitation to expedite oxidation, and that the degree of purification of the sewage depends in part on adequacy of mixing to ensure contact between the sewage and sludge surfaces and in part on the sufficiency and adequate distribution of oxygen in dissolved form to properly support chemical reactions taking place. The '349 patent does not disclose the use of high shear mixing to create microbubbles and for intimate mixing of the microbubbles with a phosphorus-containing waste.
U.S. Pat. No. 4,582,612 discloses an apparatus for treating sewage sludge by breaking the sludge into minute particles and dispersing them into an oxygen-rich pressurized atmosphere. The present invention is an atmospheric pressure process, and does not entail the disadvantages of a pressure process, such as increased material costs and lower safety.
U.S. Pat. No. 4,174,280 discloses a process for the aqueous oxidation with an oxygen-containing gas of an oxidizable material which is insoluble, immiscible, and difficult to suspend or emulsify in water, and is limited to a group consisting of motor oils, diesel fuels, explosives, and propellants.
U.S. Pat. No. 4,648,973 discloses a method to oxidize sludge with high solids content utilizing a counter-bubble reactor in which oxygen is injected into the upper part of the reactor and circulated by sludge flow only. No mechanical agitation is used.
U.S. Pat. No. 4,698,216 discloses a method for reacting phosphorus-containing material and an oxygen-containing gas, both in finely-divided form, to produce aqueous H.sub.3 PO.sub.4. The '216 patent reaction takes place under a protective aqueous layer, protecting the phosphorus from direct contact with atmospheric oxygen. The present invention actually uses air, including atmospheric oxygen, as the preferred reactive gas, and does not require a protective aqueous layer.
In addition, U.S. Pat. Nos. 3,684,461; 4,284,515; 4,402,833; 4,689,121; and 4,595,492 disclose methods for removing phosphorus from an aqueous medium. In all cases, the methods are non-oxidative and use a variety of techniques for the removal of phosphorus, including the addition of caustic soda, lime, and physical separation methods such as centrifuging, flash evaporation, and filtration. Thus it can be seen that there is a need for a low cost, fast, and efficient method and apparatus for the complete conversion of phosphorus contained in wastes to less hazardous, less toxic, and/or more useable materials.